Original article
Electromyographic Activity in the Immobilized Shoulder Girdle Musculature During Ipsilateral Kinetic Chain Exercises

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Abstract

Smith J, Dahm DL, Kotajarvi BR, Boon AJ, Laskowski ER, Jacofsky DJ, Kaufman KR. Electromyographic activity in the immobilized shoulder girdle musculature during ipsilateral kinetic chain exercises.

Objective

To quantify the electromyographic activity in the shoulder girdle musculature during ipsilateral kinetic chain exercises performed in a shoulder immobilizer in asymptomatic men.

Design

Descriptive.

Setting

Motion analysis laboratory at a tertiary care center.

Participants

Five asymptomatic male volunteers, ages 24 to 32 years.

Intervention

Fine-wire (supraspinatus, infraspinatus, upper subscapularis) and surface (deltoids, trapezii, biceps, serratus anterior) electrodes recorded electromyographic activity from each muscle during a split-stance cross-body rotation (twisting to the opposite side at high, mid, and low levels), split stance attempted ipsilateral floor touch, and attempted overhead reach. All movements were initiated from the immobilized scapula and were tested with and without a combined step.

Main Outcome Measure

Mean peak normalized (percentage of maximum voluntary contraction [%MVC]) electromyographic activity of each muscle during each exercise.

Results

For all exercises, biceps and infraspinatus activity remained low (<10% MVC), whereas upper subscapularis activity was moderate to very high (29%−68% MVC). Supraspinatus activity was low (<20% MVC) for all motions except the attempted overhead reach (23% MVC). Serratus electromyographic activity was less than 20% of MVC for all motions and was most responsive to added stepping (23%−136% MVC without stepping vs 24%−199% MVC with stepping). Cross-body rotation at lower heights progressively increased serratus activity while decreasing supraspinatus, upper trapezius, and anterior deltoid activity.

Conclusions

Based on these electromyographic data, selected kinetic chain exercises could potentially be implemented during periods of shoulder immobilization. All exercises examined could potentially be safe after superior labral anteroposterior repair, but not after subscapularis repair. All exercises, with the exception of the attempted overhead reach, could potentially be safe after supraspinatus repair, with or without concomitant infraspinatus repair. Early activation of the serratus anterior could potentially be achieved by performing cross-body rotations, particularly at lower heights.

Section snippets

Participants

Five healthy, right-hand dominant men, ages 24 to 32 years, volunteered to participate. Subjects were recruited from our institution via advertisement. The first 5 men meeting the following inclusion criteria were enrolled: (1) right-hand dominant, (2) no history of right shoulder or neck injury or pain requiring formal medical treatment or activity modification, (3) full, pain-free, bilateral shoulder range of motion at the time of enrollment, and (4) no contraindications to fine-wire

Results

Figures 4A and 4B show the mean peak electromyographic activity for the rotator cuff, biceps, and anterior deltoid muscles during each motion. With the exception of the upper subscapularis, there was relatively little variation in mean peak electromyographic activity as a function of exercise. Infraspinatus and biceps brachii activity was uniformly low and responded very little to stepping (infraspinatus, 3%−6% MVC without step vs 3%−7% MVC with step; biceps, 3%−5% MVC with or without step).

Discussion

Shoulder immobilizers are commonly used postinjury and postsurgery to rest and protect healing tissues, particularly the anterior deltoid, supraspinatus, infraspinatus, subscapularis, and/or biceps brachii. Our previous investigation suggested that deliberately performed ipsilateral scapulothoracic motions could be used during shoulder immobilization as part of the acute phase rehabilitation process in selected cases.11 Scapular depression and protraction performed with the immobilized shoulder

Conclusions

The current data suggest that early activation of the immobilized shoulder girdle musculature could potentially be safely achieved by performing specific kinetic chain exercises. The serratus anterior is perhaps the most important scapular stabilizer muscle.7, 8, 9, 23 Our results indicate that among the exercises currently investigated, cross-body rotations are best to achieve early activation of the serratus anterior. Although somewhat more selective serratus activity may be obtained by

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    Supported by the Mayo Foundation and the Physiatric Association of Spine, Sports, and Occupational Rehabilitation.

    No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated.

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